Physical Properties of Solutions

A comprehensive vocabulary review of physical properties of solutions, covering solution types, concentration units, solubility principles, colligative properties, and electrolyte behavior.

Solution

A homogeneous mixture of two or more substances.

Solute

The substance or substances present in a solution in the smaller amount(s).

Solvent

The substance present in a solution in the larger amount.

Saturated Solution

A solution that contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.

Unsaturated Solution

A solution that contains less solute than the solvent has the capacity to dissolve at a specific temperature.

Supersaturated Solution

A solution that contains more solute than is present in a saturated solution at a specific temperature, which rapidly crystallizes upon introducing a seed crystal.

Enthalpy of Solution ($\Delta H_{\text{soln}}$)

The overall enthalpy change of the solution process, given by the sum of three component interactions: solvent-solvent separation ($\Delta H_1$), solute-solute separation ($\Delta H_2$), and solvent-solute mixing ($\Delta H_3$), expressed as $\Delta H_{\text{soln}} = \Delta H_1 + \Delta H_2 + \Delta H_3$.

"Like Dissolves Like"

The empirical principle stating that two substances with similar intermolecular forces are likely to be soluble in each other; non-polar solutes dissolve in non-polar solvents, while polar and ionic solutes dissolve in polar solvents.

Percent by Mass

A concentration unit defined as the ratio of the mass of the solute to the total mass of the solution multiplied by $100\%$: $\text{\% by mass} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100\%$.

Mole Fraction ($X_A$)

A dimensionless concentration measure equal to the number of moles of a specific component ($A$) divided by the total number of moles of all components in the mixture: $X_A = \frac{\text{moles of } A}{\text{sum of moles of all components}}$.

Molarity ($M$)

The number of moles of solute dissolved per liter of solution: $M = \frac{\text{moles of solute}}{\text{liters of solution}}$.

Molality ($m$)

The number of moles of solute dissolved per kilogram of solvent: $m = \frac{\text{moles of solute}}{\text{mass of solvent (kg)}}$.

Fractional Crystallization

The separation of a mixture of substances into pure components on the basis of their differing solubilities across varying temperatures.

Henry's Law

A law stating that the solubility of a gas in a liquid ($c$) is directly proportional to the pressure ($P$) of the gas above the solution: $c = kP$, where $k$ is a temperature-dependent proportionality constant.

Colligative Properties

Properties of solutions that depend solely on the number of solute particles present in solution and not on the chemical identity or nature of those particles.

Raoult's Law

A law stating that the vapor pressure of a solvent over a solution ($P_1$) equals the mole fraction of the solvent ($X_1$) multiplied by the vapor pressure of the pure solvent ($P_1^0$): $P_1 = X_1 P_1^0$.

Ideal Solution

A solution that obeys Raoult's law across all concentrations, characterized by a total vapor pressure equal to the sum of the partial pressures: $P_T = P_A + P_B = X_A P_A^0 + X_B P_B^0$.

Positive Deviation from Raoult's Law

A condition where the total vapor pressure ($P_T$) is greater than predicted by Raoult's law because the intermolecular forces between unlike molecules ($A\text{-}B$) are weaker than the forces between like molecules ($A\text{-}A$ and $B\text{-}B$).

Negative Deviation from Raoult's Law

A condition where the total vapor pressure ($P_T$) is less than predicted by Raoult's law because the intermolecular forces between unlike molecules ($A\text{-}B$) are stronger than the forces between like molecules ($A\text{-}A$ and $B\text{-}B$).

Fractional Distillation Apparatus

A distillation setup consisting of a distilling flask, heater, fractionating column, thermometer, condenser, adapter, and receiving flask, used to separate liquid mixtures based on boiling-point differences.

Boiling-Point Elevation ($\Delta T_b$)

The difference between the boiling point of a solution ($T_b$) and the boiling point of the pure solvent ($T_b^0$), given by $\Delta T_b = T_b - T_b^0 = K_b m$.

Freezing-Point Depression ($\Delta T_f$)

The difference between the freezing point of the pure solvent ($T_f^0$) and the freezing point of the solution ($T_f$), given by $\Delta T_f = T_f^0 - T_f = K_f m$.

Molal Boiling-Point Elevation Constant ($K_b$)

A solvent-specific proportionality constant that relates boiling-point elevation to the molality of the solution, expressed in units of $^\circ\text{C}/m$.

Molal Freezing-Point Depression Constant ($K_f$)

A solvent-specific proportionality constant that relates freezing-point depression to the molality of the solution, expressed in units of $^\circ\text{C}/m$.

Osmosis

The net selective flow of solvent molecules through a porous or semipermeable membrane from a dilute solution into a more concentrated one.

Semipermeable Membrane

A membrane barrier that permits the passage of solvent molecules while preventing the passage of solute molecules.

Osmotic Pressure ($\pi$)

The pressure required to completely stop osmosis from occurring across a semipermeable membrane, calculated as $\pi = MRT$.

Isotonic Solution

A solution that has equal osmotic pressure and solute concentration compared to intracellular fluid, causing no net movement of water.

Hypotonic Solution

A solution that has a lower osmotic pressure and lower solute concentration than intracellular fluid, causing solvent to flow into the cell.

Hypertonic Solution

A solution that has a higher osmotic pressure and higher solute concentration than intracellular fluid, causing solvent to flow out of the cell.

van 't Hoff Factor ($i$)

A factor accounting for the dissociation of electrolytes in solution, defined as the ratio of the actual number of particles in solution after dissociation to the number of formula units initially dissolved: $i = \frac{\text{actual number of particles in soln after dissociation}}{\text{number of formula units initially dissolved in soln}}$.